1. Field of the Invention
The present invention is related to a bonding method which prevents wire sweep and the wire structure thereof and more particularly to the wire between the first bonding point and the second bonding point being shifted sideward to increase the intensity of the structure of the wire against the stress of the molding flood and the shift space of the wire caused by the molding flood.
2. Description of the Related Art
The conventional method of wire bonding, as shown in FIG. 1, a semiconductor device 100 having a plurality of wires 110, which connect eh first bonding pad 120 (on the chip 101) and a second bonding pad 130 (on the inner lead) to form a closed loop. The wire 110 extends upward from the first bonding pad 120 and downward to a second bonding pad 130 by bending so that the wire 110 has a high profile between the first bonding pad 120 and the second bonding pad 130. Because the high profile is mechanically supported only at the point of the bonding pad, therefore the high profile can easily be shifted by the stress of the molding flow that causes the wire to short. When the semiconductor device 100 is in the molding process, the liquified encapsulating material pushes the wires 110 the wires 110 are then shifted at a corner of the chip in an area of low wore arrangement density of the device 100 resulting wire sweeping occurs. Referring to FIG. 2, the bonding pads are arranged very close to one another at the corner of the chip resulting in a high wire arrangement density of wires 110. When the wires 110 undergo the molding flow from the molding process, wire sweeping occurs. However, it is difficult to overcome the occurrence of wire sweep by means of increasing the distance between two wires 110 because due to the requirement of small current, thus the dimension of the chip is small. Therefore, limited surface areas of the chip are provided for wire bonding. As shown in FIG. 3, when the device is in the molding process (referring to a direction shown by an arrow in FIG. 3), the corner of the chip 101 has a high wire arrangement density, which results in a deformation of wire 110 which is pushed by the molding flow. When a bending angle of the deformed wires 110 is large enough, the deformed wires 110 will come into contact with nearby wire 110 resulting in wire sweeping.
In order to overcome the above-mentioned wire sweep problem, R.O.C. Pat. Publication No. 246,245, Utility Model published on Apr. 21, 1995, discloses a structure entitled xe2x80x9cDual Wire Structure of the Semiconductor Packagexe2x80x9d. As shown in FIGS. 4 and 5, the distance between two pads of the chip 200 is 4 mil or less. When molding, two or more wires 210 are juxtaposed in this area to overcome wire sweep which can be easily caused wire shift during mold flow. This method provides an auxiliary wire against the mold flow to prevent the deformation of the wire 210 and thus prevent the wire contact problem. Therefore, Publication No. 246,245 provides double wires 210 connecting the first bonding pad 220 to the second bonding pad 230 at the corner of the chip 200 (where molding flow is maximum).
Publication No. 246,245 overcomes the wire sweep problem by means of one or more auxiliary wires juxtaposed against the mold flow. Even if the auxiliary wire, the open loop, is shifted by mold flow and makes contact with another wire, the device does not experience wire short. However, adding the auxiliary wire has two main flaws: one, it reduces the applicable surface area of the chip for the wire bonding process; two, it increases the cost and manufacturing time of products.
The present invention intends to provide a bonding method which pre-shifts the wire from the reference line of connection between the first bonding pad and the second bonding pad in a direction counter to the mold flow to increase the strength of wire structure and to form the deformation space for wire shift, thus decreasing the occurrence of wire sweep. The present invention, which utilizes the pre-shifted wire, reduces the addition of the auxiliary wire of Pat. Publication No. 246,245 in such a way as to mitigate and overcome the above problem.
The primary objective of this invention is to provide a bonding method and the wire structure thereof in which the wire between the first bonding point and the second bonding point is bent to shift aside and counter the mold flow and form a deformation space for the wire to reduce the occurrence of wire sweep.
The present invention is a bonding method that prevents wire sweep. The present invention mainly provides a pre-shifted wire between the first bonding point and the second bonding point, which is counter to a mold flow from the side. This bonding method of the present invention intensifies the strength of the wire structure and increases the deformation space of the wire sustaining mold flow. The techniques of the present invention will be disclosed in a preferred embodiment and incorporated with other ordinary skill in the art.
Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description and the accompanying drawings.